The invention relates to linear polishing, and more particularly to in-situ monitoring of linear substrate polishing operations.
It is always desirable to monitor polishing operations in-situ. For example, during chemical mechanical polishing operations, it is desirable to determine the point (end point) when a substrate layer has been polished to a desired thickness because the polishing rate may vary over time. Chemical mechanical polishing is a process by which a substrate surface is smoothed (planarized) to a substantially uniform level by a polishing pad and an abrasive slurry. A substrate to be polished is usually mounted on a rotatable carrier head and pressed against a moving polishing pad. The polishing pad typically consists of an abrasive sheet. An abrasive chemical solution (slurry) may be introduced onto the polishing pad to assist in the polishing process.
The invention features a substrate polishing scheme (apparatus and method) according to which a polishing surface of a polishing sheet is driven in a generally linear direction by a drive mechanism, a surface of a substrate is held against the polishing surface of the polishing sheet by a polishing head, and the substrate is probed through the polishing sheet by a monitoring system.
Embodiments may include one or more of the following features.
In one embodiment, the monitoring system comprises a light source configured to produce light and to direct the light through the polishing sheet to the substrate, and a detector configured to detect light reflecting from the substrate. In this embodiment, the polishing sheet includes a region that is at least semi-transparent with respect to the light produced by the light source. The polishing sheet may be formed from material that is at least semi-transparent with respect to the light produced by the light source. Alternatively, the polishing sheet may formed from material that is substantially opaque with respect to the light produced by the light source, and the polishing sheet may include a discrete region that is at least semi-transparent with respect to the light produced by the light source. The discrete region may extend substantially the length of the polishing sheet, or may extend only a limited length of the polishing sheet.
In another embodiment, the polishing surface of the polishing sheet comprises a plurality of projecting surface features. The surface features may be disposed across the polishing surface with a substantially uniform spacing between adjacent surface features, and the surface features may be sufficiently transmissive for the monitoring system to probe the substrate. Alternatively, the surface features may be disposed across the polishing surface with a substantially uniform spacing between adjacent surface features, except for a probe region of the polishing surface where the spacing between adjacent surface features is greater than the spacing at other locations to enable the monitoring system to probe the substrate.
The monitoring system may be configured to operate in coordination with the polishing head and the drive mechanism to periodically probe the substrate. A rotation mechanism may be provided to rotate the linear drive mechanism in a plane relative to the substrate.